The invention relates to a process or starting a direct-injecting internal-combustion engine, to a corresponding system, as well as to a corresponding motor vehicle.
The internal-combustion engine of a motor vehicle is normally started by a starter motor, such as a pinion starter. In the case of hybrid vehicles, thus, in the case of motor vehicles which, in addition to the internal-combustion engine, have at least one additional electric machine, this electric machine can take over the function of the starter motor and the latter can therefore be eliminated.
It is an object of the invention to indicate a further process as well as a corresponding system for starting an internal-combustion engine.
According to the invention, a process for starting a direct-injecting internal-combustion engine comprises at least the following steps. Triggering a separate drive, whereby the crankshaft of the internal-combustion engine, by way of mechanical driving devices, which comprise an adjusting mechanism having the separate drive is provided for driving a camshaft of the internal-combustion engine, for adjusting the camshaft in order to cause by way of the adjusting mechanism an angular-position change between the crankshaft and the camshaft until the separate drive of the adjusting mechanism rotates the crankshaft by way of the mechanical driving devices and thus a working medium is compressed in at least one cylinder of the internal-combustion engine by means of the piston. Then, the process includes determining the position of the pistons by using position determining devices and thus identifying the cylinder of the internal-combustion engine in which the working medium is compressed. Further, the process includes injecting fuel into this cylinder when the cylinder is in the proximity of its upper dead center, for starting the internal-combustion engine. In other words, the invention utilizes the separate drive of a camshaft adjusting device for starting the internal-combustion engine. For this purpose, during a stoppage of the internal-combustion engine, an “inverse” operation of the camshaft adjusting device takes place for a short time in that its separate drive is therefore utilized for driving the crankshaft of the internal-combustion engine by way of the mechanical driving devices. The separate drive of the camshaft adjusting device is therefore quasi reworked as a starter motor. In this case, the camshaft adjusting device adjusts only the control timing of the camshaft with respect to the crankshaft; the valve opening period and the valve stroke of the internal-combustion engine are not changed by this phase adjustment. The invention is based on the recognition that the angular-position change between the crankshaft and the camshaft caused by means of the separate drive, in each case, affects that shaft which has the lower moment of resistance. In the case of the moment of resistance, for example, the friction, the moments of compression for compressing the cylinders or the operating moments of the valves at the camshaft are to be taken into account.
Particularly preferably, the separate drive is triggered in the first step until a cam rests approximately on the stop of a valve of the internal-combustion engine, and is subsequently triggered further, in which case the cam resting on the stop of the valve now supports itself on this valve and thereby blocks the camshaft, whereby the separate drive now rotates the crankshaft by way of the mechanical driving devices. In the case of a corresponding design, this permits a reliable use of the invention.
In a first preferred embodiment of the invention, the internal-combustion engine is provided as a direct-injecting diesel engine, in which case diesel fuel is injected in the proximity of the upper dead center, which diesel fuel ignites itself and the internal-combustion engine is started in this manner.
In a second preferred embodiment, the internal-combustion engine is provided as a direct-injecting Otto engine, in which case Otto fuel is injected in the proximity of the upper dead center and an ignition operation is triggered and the internal-combustion engine is started in this manner. Naturally, the internal-combustion engine may also be provided as a lean-mix engine (stratified-charge or Disotto engine).
Driving belts or toothed belts or a chain drive are provided as particularly reliable mechanical driving devices. These permit a low-maintenance drive of the camshaft by way of the mechanical driving device by the crankshaft of the internal-combustion engine, and thereby also the start of the internal-combustion engine according to the invention.
In this case, the driven camshaft may be provided as an inlet or outlet camshaft of the internal-combustion engine. As a function of the type of internal-combustion engine, a flexible use of the invention is thereby obtained.
Crankshaft sensors were found to be successful as the position determining devices. By way of corresponding projections or notches of the crankshaft, reliable conclusions can then be drawn about the position of the crankshaft and thus about the power cycle of the individual cylinders of the internal-combustion engine. In particular, it can also be determined when a cylinder is situated in the proximity of its upper dead center in order to thus provide an injection of fuel for starting the internal-combustion engine.
In a preferred embodiment, the separately drivable adjusting mechanism comprises a transmission, especially a planetary transmission. When the space requirements are low, a sufficient torque can also be applied in the case of a separate drive with a relatively low-power design in that a corresponding transmission ratio is used.
Particularly preferably, the separate drive of the adjusting mechanism is implemented electrically, particularly as an electric motor. Naturally, other types of drives may also be provided, such as an electro-hydraulic drive. In each case, a reliable operation of the separate drive is necessary when the internal-combustion engine is idle.
The process according to the invention utilizes the separately drivable adjusting mechanism for rotating the crankshaft. However, normally only a limited adjusting range is provided in order to protect the valves of the internal-combustion engine. As a result, it is advantageous to move the separately drivable adjusting mechanism into an end stop position when the internal-combustion engine is switched off. The reason is that, when the internal-combustion engine is started, according to the process of the invention, the entire adjusting range of the separately drivable adjusting mechanism will be available. In this case, the forward or rearward end stop of the separately drivable adjusting mechanism can be provided as end stop positions. In other words, as a result of the process according to the invention, the engine can be started in the forward or backward direction.
In a particularly preferred embodiment of the invention, the internal-combustion engine is constructed as a multi-bank engine with respectively assigned, separately driven adjusting mechanisms, the adjusting mechanisms being controlled in the same direction, for the addition of the torques transmitted by the separate drives—supported, for example, at the respective valves—by way of the mechanical driving devices to the crankshaft. The addition of the torques may be provided successively or simultaneously. With each triggered separate drive of a respective adjusting mechanism of a camshaft, the torque is increased that is transmitted to the crankshaft by way of the mechanical driving devices. As a result, also the torques for the rotation of the crankshaft are correspondingly increased and a reliable start of the internal-combustion is ensured.
In this case, the adjusting mechanism may also comprise a torque support which ensures a supporting, for example, in the direction opposite to the rotating direction, and thus the rotation of the crankshaft. For this purpose, for example, a free wheel may be provided on the camshaft or the crankshaft.